包覆複合材料的地埋U型管熱傳性能分析

Abstract

國立臺灣大學機械工程學系碩士論文 論文題目：包覆複合材料的地埋U型管熱傳性能分析 指導教授：陳希立 博士 作 者：熊冠丞 中華民國一百零四年七月 淺層溫能已行之有年，U型管更是常被利用的地埋熱交換器，但因其特殊的幾何形狀，部分熱能可能由較高溫之下降支管，流向相鄰之上昇支管內，使U型管出口溫度上昇，造成熱傳性能的降低，此即熱短路或熱回流現象。 改善熱短路現象的方法有很多，像是拉長兩管間距或是在鑽井中央加裝擋熱隔板都是可行的方法。但挖設地埋管也不是一件簡單的工程，想擴大鑽井直徑勢必會耗費大量成本。現有一個新型的U型地埋管專利設計，在上升端包覆一層絕熱材，以阻絕熱短路的影響，再在其上包覆一層導熱材，擴大土壤可用的熱交換區域。 本實驗透過FLUENT軟體模擬高緯度地區利用淺層溫能製暖的情境，觀察入出口水溫的變化，並透過縮小尺度的迷你實驗來驗證此一設計的可行性。透過模擬的結果發現，此一新型的U型地埋管專利設計會有比原始的U型管較大的入出口溫差，但效果並不顯著。此外，本研究進行的實驗結果與模擬的結果並不相符，表示此一設計在實際應用面還有很大的改進空間，並不建議採用。

Shallow Geothermal Energy has been introduced to human society for decades, and U-type Borehole Heat Exchanger is one of the most frequently used ground source heat exchangers. However, the downward and upward pipe will interfere with each other and cannot obtain the anticipated Coefficient of Performance due to its special geometry shape. This phenomenon is so called “thermal short circuit”. There are many ways to modify the phenomenon of “thermal short circuit”. For instance, expanding the distance between two pipes or adding an adiabatic board in the middle of the borehole are both applicable ways to improve it. But it is not easy to expand the diameter of the borehole, especially when the construction is really deep. Now there is a new patent design for the U-type borehole heat exchanger. This research simulates the scenario of the high latitude area by FLUENT software and does a mini-dimension experiment to verify if this new design is applicable. Through the result of FLUENT simulation, the new design of the U-type borehole heat exchanger has a slightly better result while the experiment has a totally opposite result. Therefore this new patent design is not recommendable.